Congo fever and dengue similarities: ICMR calls for review of dengue cases

2011

Syed Akbar

Hyderabad, Feb 3: With many doctors unable to distinguish between dengue and Congo fever based on symptoms, the Indian Council of Medical Research has asked health officials to review cases of fever that have been declared as dengue, particularly in rural areas.

The ICMR suspects that some of the fever cases that had been diagnosed as dengue may actually be those of Congo fever. The State and several parts of the country have witnessed many cases of death related to dengue. The emergence of a new serotype of dengue virus, dengue-4 or Denv-4, has further complicated the task of doctors, many of whom had no first hand experience of treating patients suffering from Crimean-Congo haemorrhagic fever.

The symptoms of Denv-4, which was first reported in Hyderabad in 2007, and those of Congo fever interlap making it difficult to diagnose the case at first sitting. Since Congo fever had not been reported in the country prior to January this year, many doctors suspect complicated cases of fever as those of dengue. In both the cases haemorrhage or bleeding is common. The fatality rate of Congo fever, however, is higher. Common dengue is mild, while cases related to serotype Denv-4 may turn out to be fatal.

Cases of dengue haemorrhagic fever have increased in the country since 1990 after the common dengue virus underwent mutation leading to change in the virus "lineage especially with regard to Denv-2 and Denv- 3", according to Dr D Cecilia of the National Institute of Virology. Dr Cecilia's team has recently found re-emergence of Denv-4 in Maharashtra after a gap of 35 years. Denv-4 cases have thus far been rare.

"It's true that unless thorough clinical investigation is done, it is difficult to differentiate between dengue and Congo fevers initially because the symptoms of both are almost the same such as haemorrhage and fever," says Dr K Subhakar of Government Chest Hospital in the city. He agrees that the blood samples collected need to be studied properly to find out whether it’s a dengue virus or Congo fever virus.

While the NIV has called for a close monitoring of Denv-4 cases, senior physician of Care Hospitals Dr S Vijay Mohan accepts that some Congo fever cases are being passed off as dengue fever mainly because of ignorance about this new disease.

"Except the four cases in Gujarat, it hasn’t been found anywhere in India. Since symptoms of the two diseases are more or less the same, only a blood test can reveal whether it’s dengue fever or some other kinds of viral fever. There are hundreds of country-specific viruses, causing unknown fevers. Unless, a specific test to detect the Congo fever virus is conducted, it
will be difficult to point out the nature of the fever causing virus," he adds.

Even as the ICMR has suggested a review of dengue cases from rural areas, a study by NIV scientists warns that the high degree of diversity in the envelope gene observed for the Denv-4 viruses circulating in the subcontinent indicates that the "serotype is evolving". And if this happens, there may be newer dengue strains.